What is Qo. S (contd) ? q These parameters can be measured at several granularities: q “micro” flow, aggregate flow, population. q Qo. S considered “better” if q a) more parameters can be specified q b) Qo. S can be specified at a fine-granularity. q Qo. S spectrum: Best Effort Leased Line Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6

Fundamental Problems Scheduling Discipline FIFO B B q In a FIFO service discipline, the performance assigned to one flow is convoluted with the arrivals of packets from all other flows! q Cant get Qo. S with a “free-for-all” q Need to use new scheduling disciplines which provide “isolation” of performance from arrival rates of background traffic Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7

Bit-by-bit Round Robin q Single flow: clock ticks when a bit is transmitted. For packet i: q Pi = length, Ai = arrival time, Si = begin transmit time, Fi = finish transmit time q Fi = Si+Pi = max (Fi-1, Ai) + Pi q Multiple flows: clock ticks when a bit from all active flows is transmitted round number q Can calculate Fi for each packet if number of flows is known at all times q. This can be complicated Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19

Putting it together: Parekh-Gallager theorem Let a connection be allocated weights at each WFQ scheduler along its path, so that the least bandwidth it is allocated is g q Let it be leaky-bucket regulated such that # bits sent in time [t 1, t 2] <= g(t 2 - t 1) + q Let the connection pass through K schedulers, where the kth scheduler has a rate r(k) q Let the largest packet size in the network be P q Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 22

Significance P-G Theorem shows that WFQ scheduling can provide end-to-end delay bounds in a network of multiplexed bottlenecks q WFQ provides both bandwidth and delay guarantees q Bound holds regardless of cross traffic behavior (isolation) q Needs shapers at the entrance of the network q Can be generalized for networks where schedulers are variants of WFQ, and the link service rate changes over time q Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 23

Call Admission Session must first declare its QOS requirement and characterize the traffic it will send through the network q R-spec: defines the QOS being requested q T-spec: defines the traffic characteristics q A signaling protocol is needed to carry the Rspec and T-spec to the routers where reservation is required; RSVP is a leading candidate for such signaling protocol q Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 27

Call Admission q Call Admission: routers will admit calls based on their R-spec and T-spec and base on the current resource allocated at the routers to other calls. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 28

Differentiated Services (diffserv) Intended to address the following difficulties with Intserv and RSVP; q Scalability: maintaining states by routers in high speed networks is difficult sue to the very large number of flows q Flexible Service Models: Intserv has only two classes, want to provide more qualitative service classes; want to provide ‘relative’ service distinction (Platinum, Gold, Silver, …) q Simpler signaling: (than RSVP) many applications and users may only w ant to specify a more qualitative notion of service. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute q 29

Packet format support Packet is marked in the Type of Service (TOS) in IPv 4, and Traffic Class in IPv 6: renamed as “DS” q 6 bits used for Differentiated Service Code Point (DSCP) and determine PHB that the packet will receive q 2 bits are currently unused q Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 32

Real-Time Protocol (RTP) Timestamp: 32 bytes; gives the sampling instant of the first audio/video byte in the packet; used to remove jitter introduced by the network q Synchronization Source identifier (SSRC): 32 bits; an id for the source of a stream; assigned randomly by the source q Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 37

Using a Streaming Server q q q Web browser requests and receives a Meta File (a file describing the object) Browser launches the appropriate Player and passes it the Meta File; Player contacts a streaming server, may use a choice of UDP vs. TCP to get the stream Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 41

Receiver Adaptation Options q q If UDP: Server sends at a rate appropriate for client; to reduce jitter, Player buffers initially for 2 -5 seconds, then starts display If TCP: sender sends at maximum possible rate; retransmit when error is encountered; Player uses a much large buffer to smooth delivery rate of TCP Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 42

H. 323 is an ITU standard for multimedia communications over best-effort LANs. q Part of larger set of standards (H. 32 X) for videoconferencing over data networks. q H. 323 includes both stand-alone devices and embedded personal computer technology as well as point-to-point and multipoint conferences. q H. 323 addresses call control, multimedia management, and bandwidth management as well as interfaces between LANs and other networks. q Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 43